Interaction of the amalgam used in dental restorations with the oral environment causes changes which contribute to the deterioration and failure of the restorations. The interaction is electrochemical in nature and the understanding of the mechanism and effects on properties are essential for the development of better materials. In this program the emphasis in on high-copper amalgams which have shown best clinical performance. In the study of the mechanism of corrosion the electrochemical stability of coppertin and similar phases will be examined with special attention to the effect of mercury. The access of the electrolyte to the corrosion-susceptible phase within the structure will be investigated. Acceleration of corrosion by mechanical abrasion will be studied. The experimental techniques will include measurements of polarization characteristics of electrodes, coulometry, optical and scanning electron microscopy, and x-ray analysis. The investigation of the effects of corrosion on the mechanical properties will be focused on the causes of the observed loss of strength and the role of corrosion products, the kinetics of the deterioration under load, and formulation of quantitative relationships which would predict the failure of restorations in vivo. Changes in the appearance of restorations---tarnishing---which are caused by the formation of sulfide films, will be investigated by electrochemical techniques with the objective of determining the kinetic parameters of the reactions and their dependence on composition and structure.